Light environment created by a lighting device has significant psychological and biological influences on humans. Therefore, appropriate design of light environment is one of basic elements to attain healthy and comfortable living environment.
On the other hand, similar to other electrical appliances, the lighting device is also required to have an energy saving function.
As an example of the energy saving function of a conventional lighting device, Japanese Patent Laying-Open No. 11-204271 (Patent Document 1) proposes a method of gradually lowering, from the start point of lighting of lighting load, output of lighting load to reduce brightness to a prescribed light intensity.